There is no right or optimal place to hit a ball on the tennis racket that applies to everyone. Everyone plays differently and looks to get a different type of result out of each shot.
I'm definitely no expert on the physics of tennis, but I can tell you from experience, where on your racket you should aim to hit the ball.
The part labeled Node, is probably the best for when you your trying to roll a nice spin ball off your racket.
The part labeled COP, is the opposite, and should be used when hitting a slice ball.
However, while the bottom area of the racket (labeled Best Bounce in your image), is usually used for a flat ball because the ball doesn't need much room to roll on your racket, I would stay away from it in many cases. If you're a player who enjoys smacking that ball when you're on the offensive, then go ahead. But it's not always the best for Touch. That area of the racket is usually unpredictable and isn't optimal for a volley or drop...